Occipital Lobe

• Videos: – Brain modules 8,9,10, 11– Consciousness- Blindsight

EYEEYE

Rods ConesRods Cones

Receptors:Receptors: rods and cones rods and cones

• 120 million120 million

• peripheryperiphery

• sensitivitysensitivity

• night visionnight vision

• 8 million8 million

• centralcentral

• acuityacuity

• color visioncolor vision

Anatomical Pathway in the RetinaAnatomical Pathway in the Retina

Retina

Optic Nerve Exits

Locating Blindspot

Stare at single star for 60-90 sec

Color-Deficient Vision

• People who suffer red-green blindness have trouble perceiving the number within the design

• axons of retinal ganglion cells

• 106 axons of retinal ganglion cells from each eye converge at optic chiasm and hemidecussate

• Retinal Ganglion Cells project to:– 20% project to the

Superior Colliculus (retinotectal/pulvinar pathway) “where it is”

– 80% of the axons of retinal ganglion cells project to the Lateral Geniculate Nucleus (retinocortical pathway) “what it is”

Occipital Lobe

The Lateral Geniculate Nucleus of Thalamus

Central Visual Pathways: the Visual Cortex

• Visual Cortex

• Cortical magnification factor -- foveally weighted: cortical volume is related to retinal area’s spatial resolution

• -- central 10 degrees of VF around fovea maps to 80% of V1 (primary visual cortex)

Receptive Field Properties of Cortical NeuronsBased on Hubel and Wiesel

Simple Cells•orientation selective

• Response to spotsOn - Off regions

•Responds to edges

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Complex Cells•movement sensitive•can’t predict response fromstatic on off receptive fields

Hypercomplex Cells•end stopping

Form Perception

• LGN - Parvocellular System

• V1 (Interblobs) ---> V2 ---> V3

• Inferotemporal Cortex (MT)– complex stimuli - grandmother cells– Damage leads to visual agnosia

Movement Perception

• Rods

• LGN - Magnocellular system

• V1 ---> V2 ---> V5

• V5: middle temporal lobe (MT)– Damage - akinetopsia (unable perceive motion)

High-level Visual Processing

• V1- elementary properties detected (edge,etc)

• V2 -input from V1• divergence of color, form,

location

• V3 - shape (form) - inferotemporal

• V4 - color - lingual & fusiform gyri

• V5 - motion - midtemporal• PPC - location - posterior

parietal cortex ~

Striate Cortex (V1)• Many more dimensions in which

receptive fields may be described – or “tuning”– Receptive field size– Sensitivity to motion?– Sensitivity to chages in wavelength?– Orientation selectivity?– Occular dominance?

Striate Cortex (V1)• Projection to V1 from magnocellular

portion of V1 – Motion sensitivity (direction and velocity)– Orientation sensitivity– Disparity sensitivity

• Projection to V1 from parvocellular portion of V1 – Wavelength sensitivity– Orientation sensitivity– Disparity sensitivity

V2 – three categories• Pale stripes

– Wavelength sensitivity– Orientation sensitivity– Disparity sensitivity

• Thin stripes– Wavelength sensitivity

• Thick stripes– Motion sensitivity– Orientation sensitivity– Disparity sensitivity

V4 – recordings (Color)V4 – recordings (Color)Stimuli –light patches of different wavelengthsStimuli –light patches of different wavelengths

Neural responseNeural response

MT – recordings (Form)MT – recordings (Form)stimulistimuli

Neural responseNeural response

eyetracking